Re: Reason why "nocache" option is not displayed in "mount"?

Am 2024-03-09 06:07, schrieb Warner Losh:

> On Thu, Mar 7, 2024 at 1:05 PM Jamie Landeg-Jones <jamie@catflap.org> 
> wrote:
> 
>> Alexander Leidinger <Alexander@Leidinger.net> wrote:
>> 
>>> Hi,
>>> 
>>> what is the reason why "nocache" is not displayed in the output of
>>> "mount" for nullfs options?
>> 
>> Good catch. I also notice that "hidden" is not shown either.
>> 
>> I guess that as for some time, "nocache" was a "secret" option, no-one
>> update "mount" to display it?
> 
> So a couple of things to know.
> 
> First, there's a list of known options. These are converted to a 
> bitmask. This is then decoded and reported by mount. The other strings 
> are passed to the filesystem directly. They decode it and do things, 
> but they don't export them (that I can find). I believe that's why they 
> aren't reported with 'mount'. There's a couple of other options in 
> /etc/fstab that are pseudo options too.

That's the technical explanation why it doesn't work. I'm a step further 
since initial mail, I even had a look at the code and know that nocache 
is recorded in a nullfs private flag and that the userland can not 
access this (mount looks at struct statfs which doesn't provide info to 
this and some other things).

My question was targeted more in the direction if there is a conceptual 
reason or if it was an oversight that it is not displayed. I admit that 
this was lost in translation...

Regarding the issue of not being able to see all options which are in 
effect for a given mount point (not specific to nocache): I consider 
this to be a bug.
Pseudo options like "late" or "noauto" in fstab which don't make sense 
to use when you use mount(8) a FS by hand, I do not consider here.

I'm not sure if this warrants a bug tracker item (which maybe nobody is 
interested to take ownership of), or if we need to extend the man pages 
with info which option will not by displayed in the output of mounted 
FS, or both.

Bye,
Alexander.

-- 
http://www.Leidinger.net Alexander@Leidinger.net: PGP 0x8F31830F9F2772BF
http://www.FreeBSD.org    netchild@FreeBSD.org  : PGP 0x8F31830F9F2772BF